1. Field of the Invention
The present invention relates to a carbon nanofiber-dispersed resin fiber-reinforced composite material in which a resin having carbon nanofibers dispersed therein is impregnated into a laminated fiber reinforcement.
2. Description of the Related Art
Conventionally, fiber-reinforced composite materials are manufactured by impregnating a resin as a matrix into a laminate of fiber reinforcement made of a fiber woven material (e.g. a carbon fiber woven fabric) comprising carbon fibers, glass fibers or the like. Such fiber-reinforced composite materials are light in weight, and moreover have extremely high strength in-plane loading, in particular in the direction of tension of the fibers direction in the woven fabric, and thus have excellent specific strength and specific modulus; utilizing such properties, such fiber-reinforced composite materials are widely used as structural materials in aircraft and space equipment, and also in general industry.
However, this type of fiber-reinforced composite material has highly anisotropic properties, with the strength in a direction perpendicular to the laminate planes being extremely low compared with the strength within the laminate planes, which is generally the direction in which the fibers extend. In such a laminate type fiber-reinforced composite material, the strength of the fibers contributes little to the strength of the composite material in directions other than within the laminate planes, and hence breakage of laminate type composite materials related to the strength dependent on the resin is critical occasionally. That is, in a fiber-reinforced composite material as described above, even though the in-plane strength can be improved by reinforcing the fiber reinforcements, the strength with regard to the form of breakage dependent on the strength of the resin cannot be improved, and hence this resin-dependent strength may determine the overall strength of the fiber-reinforced composite material.
The interlaminar strength for a laminate type composite material is a representative strength dependent on the strength of the resin. Attempts have thus been made to increase the interlaminar strength using techniques such as improving or modifying the resin, or threading Kevlar or carbon yarn through the fiber reinforcement layers. However, in the case of a composite material that has such yarns that thread through the fiber reinforcement layers, stress is prone to being concentrated around the holes where yarns are threaded through the thickness of reinforcements, and hence a drop in the strength within the laminate planes may be brought about.
On the other hand, a method in which carbon nanotubes are dispersed in an epoxy resin has been disclosed (e.g. Sean Spindler Ranta and Charles E. Bakis, ‘Carbon Nanotube Reinforcement of a Filament Winding Resin’ (USA), 47th International SAMPE Symposium Proceedings, May 12 to 16, 2002, p. 1775 to 1787). This epoxy resin having carbon nanotubes dispersed therein is used in filament winding. However, this attempt was concluded that the carbon nanotubes dispersed resin did not affect the mechanical properties of the filament winding composites.